1. FIELD OF THE INVENTION
The invention relates to a process for producing individual cams from cast material for incorporation into assembled camshafts.
2. DESCRIPTION OF THE PRIOR ART
Assembled camshafts of the type in which tubes form the basic shaft member are advantageous from the point of view of weight. Steel cams, irrespective of the method used to fix them to the tube, e.g. shrinking, hydraulic deformation of the tube, or other methods, do not cause any fixing problems. However, as a rule, their tribological properties are not the most favorable for certain cam followers, e.g. bucket tappets or rocker arms, irrespective of the material from which the latter are formed. On the other hand, cast cams have good running characteristics, especially if they are provided with a hard, wear-resistant surface layer, but because of the risk of cracking they cause problems when being fixed to a tube. In particular, this is so with cams made of chilled cast iron with a ledeburitic surface layer which is too brittle for hydraulic expansion so that the cams burst during plastic deformation.
Cams made of malleable cast iron with a ledeburitic surface layer produced by remelting hardening are more suitable, but the process involved is complicated and expensive so that the production cost of the cams is too high.
Cast cams with an elongatable structure, such as malleable cast iron or spheroidal graphite cast iron subjected to induction surface hardening, are acceptable from a cost point of view. However, after hardening such cams only have a martensitic surface whose tribological properties are not as good as those of a ledeburitic surface.